in reply to {} vs do{}

do BLOCK and naked BLOCK's are completely unrelated. The documentation for do BLOCK is illuminating: 
Not really a function. Returns the value of the last command in the se
+quence of commands 
indicated by BLOCK. When modified by a loop modifier, executes the BLO
+CK once before testing 
the loop condition. (On other statements the loop modifiers test the c
+onditional first.) 

do BLOCK does not count as a loop, so the loop control statements next
+, last, or redo cannot 
be used to leave or restart the block. See the perlsyn manpage for alt
+ernative strategies.

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Naked BLOCK's on the other hand do not return values, cannot be used with loop modifiers, but can use loop control statements. Both naked BLOCK's and do BLOCK establish a new lexical scope within the BLOCK, however. 

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print

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Re: Re: {} vs do{}
by scott (Chaplain) on Jul 05, 2001 at 01:34 UTC

    Hmmmm ... what about this: 

    open( FH1 , '>foo' );
open( FH2 , '>bar' );

@fhs = ( FH1 , FH2 );

print { $fhs[ $_ % 2 ] } "$_\n" for ( 1 .. 10 );

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    which does actually put odds in one file and evens in another.

    I understood this as the BLOCK returning the last value. Is something else going on?

    Scott 'Confused in Indiana' Crittenden
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      the print BLOCK LIST form is, I suspect, analagous to something like map BLOCK list, where the BLOCK is converted into an anonymous sub which returns the value of the last expression in the block. These are syntactically different from naked BLOCKs. You can also get this behaviour with subroutine prototypes: 
      sub MySub (&\@) {
  ...
}

MySub { # do something, return a value } @list;

      [download]
         MeowChow                                   
               s aamecha.s a..a\u$&owag.print
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      The "indirect object" uses a block for its syntax, and is a different rule than a general block in the middle of an expression.
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